Heart Block (1st, 2nd, 3rd degree)

Question 1

Definition (1st)

Answer 1

prolonged conduction through the AV node

Question 2

Definition (2nd)

Answer 2

o Mobitz Type I (Wenckebach): progressive prolongation of AV node conduction culminating in one atrial impulse failing to be conducted through the AV node. The cycle then begins again.

o Mobitz Type II: intermittent or regular failure of conduction through the AV node. Also defined by the number of normal conductions per failed or abnormal one (e.g. 2:1 or 3:1)

Question 3

Definition (3rd)

Answer 3

no relationship between atrial and ventricular contraction. Failure of conduction through the AV node leads to ventricular contraction generated by a focus of depolarisation within the ventricle

Question 4

Epidemiology

Answer 4

250,000 pacemakers are implanted every year and they are mostly for heart block

Question 5

Aetiology/risk factors

Answer 5

· MI or ischaemic heart disease (MOST COMMON)
· Infection (e.g. rheumatic fever, infective endocarditis)
· Drugs (e.g. digoxin)
· Metabolic (e.g. hyperkalaemia)
· Infiltration of conducting system (e.g. sarcoidosis)
· Degeneration of the conducting system

Question 6

Presenting symptoms

Answer 6

· 1st Degree - asymptomatic

· 2nd Degree - usually asymptomatic

· Mobitz Type II and 3rd Degree - may cause Stokes-Adams Attacks (syncope caused by ventricular asystole)
o May also cause dizziness, palpitations, chest pain and heart failure

Question 7

Signs on physical examination

Answer 7

· Often NORMAL

· Check for signs of a potential cause of heart block

· Complete Heart Block
o Slow large volume pulse
o JVP may show cannon a waves
· Cannon A Waves: waves seen occasionally in the jugular vein of humans with certain cardiac arrhythmias. This occurs when the atria and ventricles contract simultaneously

· Mobitz Type II and 3rd Degree Heart Block
o Signs of reduced cardiac output (e.g. hypotension, heart failure)

Question 8

Investigations (ECG)

Answer 8

· ECG - GOLD STANDARD

o First Degree - fixed prolonged PR interval (> 0.2 s)

o Mobitz Type I (Wenckebach) - progressively prolonged PR interval, culminating in a P wave that is NOT followed by a QRS complex. The pattern then begins again. ‘Going, going, gone’.

o Mobitz Type II - intermittently a P wave is NOT followed by a QRS. There may be a regular pattern of P waves not followed by QRS (e.g. 2:1 or 3:1)

o Complete Heart Block - no relationship between P waves and QRS complexes. If QRS is initiated in the:
· Bundle of His - narrow complex
· More distally - wide complex and slow rate (~ 30 bpm)

Question 9

Investigations (other)

Answer 9

· CXR
o Cardiac enlargement
o Pulmonary oedema

· Bloods
o TFTs
o Digoxin level
o Cardiac enzymes
o Troponin

· Echocardiogram
o Wall motion abnormalities
o Aortic valve disease
o Vegetations

Question 10

Management plan (chronic block)

Answer 10

o Permanent pacemaker is recommended in:

· Complete heart block
· Advanced Mobitz Type II
· Symptomatic Mobitz Type I

Question 11

Management plan (acute block)

Answer 11

o If associated with clinical deterioration use IV atropine

o Consider temporary (external) pacemaker

Question 12

Possible complications

Answer 12

· Asystole
· Cardiac arrest
· Heart failure
· Complications of any pacemaker inserted

Question 13

Prognosis

Answer 13

· Mobitz Type II and 3rd degree block usually indicate serious underlying cardiac disease